The functional mobility and quality of life of patients who have suffered a spinal cord injury or stroke can often be improved with a rehabilitation technique termed treadmill training, in which mechanical gait assistance is delivered either by human therapists or powered exoskeletons. Unfortunately, therapist-assisted treadmill training is labor intensive, while powered exoskeletons may be prohibitively expensive for many clinics and may deliver assistance in a way that does not maximize patient recovery. In addition, both of these methods restrict patients to walking on a treadmill in a clinical setting, rather than walking over ground in a more functionally relevant context. The long-term goal of the proposed project is to develop an innovative gait rehabilitation device that is low-cost and more effective than current rehabilitation techniques. If successful, populations with limited gait function would be provided a more affordable method of gait rehabilitation that could allow them to practice assisted walking in more real world, non-clinical situations. We have developed a novel passive elastic exoskeleton based on simulations of a dynamic walking model, a strategy which has proven successful in the design of walking robots that are much cheaper and more energetically efficient than traditionally engineered bipedal robots. We hypothesize that our passive exoskeleton will provide mechanical assistance that will make walking easier, thus reducing the muscle activity and energetic cost required during gait. The specific aim of the current proposal is to optimize the design of our passive elastic exoskeleton, and determine if healthy human subjects are able to adapt their walking patterns to the resultant mechanical assistance, as evidenced by significant decreases in muscle activity and energetic cost. We will perform a series of four experiments which will investigate the effects of varying the parameters of our passive exoskeleton design on the gait of healthy subjects, with the goal of optimizing effective gait assistance. These experiments will also provide insight into the process by which healthy humans adapt to a novel mechanical context during gait. We anticipate that our optimized device will make walking significantly easier, allowing a 10% decrease in energetic cost and a 30% decrease in the muscle activity powering leg swing. In addition to possibly motivating the development of a low-cost gait assistive device for patients with moderate locomotor limitations, the findings of the proposed project may also suggest more efficient methods for controlling gait which could be useful in the improvement of powered exoskeletons for patients with more severe limitations. PUBLIC HEALTH RELEVANCE: Gait rehabilitation can often improve the functional mobility of patients who have suffered a stroke or spinal cord injury, but existing rehabilitation techniques are labor intensive or expensive. We propose the development of a low-cost mechanical device that will make walking easier for these patients, allowing them to reap the benefits of gait rehabilitation while practicing walking under natural conditions. The first step in this process is testing whether our device assists walking in healthy subjects, as indicated by reductions in energetic demand and muscle activity of the legs.